Prepending the message with a delimiter (size varint) is pretty common, even part of the reference Java implementation: https://protobuf.dev/reference/java/api-

Prepending the message with a delimiter (size varint) is pretty common, even part of the reference Java implementation: https://protobuf.dev/reference/java/api-docs/com/google/protobuf/MessageLite.html#writeDelimitedTo-java.io.OutputStream- https://protobuf.dev/reference/java/api-docs/com/google/prot...